The present invention relates to an epicyclic speed reducing transmission having a first set of conjugate epitrochoidal-like and hypotrochoidal-like shaped races and a first set of rollers disposed in these races for transmitting torque therebetween to achieve a first speed reduction, as well as a second conjugate set of epi- and hypo-trochoidal-like shaped races and a second set of rollers disposed in these latter races for transmitting torque therebetween to achieve a second speed reduction. One of the races of the first set is restricted from rotating, thus forming a stator race.
Such a transmission utilizes an eccentric cam fixedly connected to an input which orbits one of the races of each of the sets of conjugate races as the input is rotated. The eccentric cam is sized so as to normally impose a load on the first and second sets of rollers, and, specifically, on those rollers on either side of a top dead center position of the cam. As the eccentric cam orbits the races, the race of the first conjugate set of races which is not maintained rotationally stationary is rotated due to torque transmitted by the first set of rollers so as to achieve the first speed reduction. One of the races of the second set of races is coupled to the rotating race of the first set of races and rotates therewith, and the other race of the second set of races is caused to rotate at a second speed reduction due to the torque transmitted between the races of the second set by the second set of rollers. If the conjugate trochoidal races, their corresponding set of rollers, and the input shaft eccentric were made to their theoretical dimensions, no clearance would exist between these elements when assembled. If the set of rollers or the conjugate trochoidal race profiles are formed so as to deviate from their theoretical size in the direction of increasing radial clearance, the internal epitrochoidal-like race could move in the radial direction with respect to a fixed hypotrochoidal-like race because of that clearance. The radial clearance is the total distance that the epitrochoidal-like race can be displaced in a radial direction for a conjugate set consisting of an epitrochoidal-like race, a hypotrochoidal-like race, and rollers.
In such a transmission, it has been conventional to maintain the first radial clearance (between the first set of rollers and the first conjugate set of races) equal to the second radial clearance (between the second set of rollers and the second set of races). Such transmissions oftentimes do not run as smoothly as desired.